Core swactor now compiles for wasm32-unknown-unknown:
- Added `wasm` feature flag (bundles no_random + web-time)
- Platform-aware Instant: web_time::Instant on wasm, std::time on native
- cfg-gated Runtime::run() and RuntimeHandle (thread::spawn unavailable
on wasm32 — browser crate provides Web Worker-based alternative)
- Validated: crossbeam-queue, atomics, Mutex, RwLock, thread parking all
work on wasm32 with atomics target feature
- Updated crates/wasm/ to use new `wasm` feature
Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski
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